When exploring for hydrocarbons in waters subject to very rigid environmental requirements and with the requirements of zero pollution, new overall concepts and solutions must be developed in order to satisfy such environmental and political requirements. The concept for zero pollution requires a total and complete barrier solution against the surrounding sea and the marine life, covering all types of drilling and production spillage, including a blow out, pollution, spillage from the drilling system and other unintentional accidents. Such a concept must ensure that drilling as well as production operations may be performed without any type of environmental effects directly or indirectly on the waters where the platforms are installed.
For conventional type of exploration of hydrocarbons, such as drilling or maintenance operations of production wells, situations may occur where an uncontrolled blow-out may occur and where the hydrocarbons from such blow-out will end directly into the sea. When production and pre-caution barriers have failed, only traditional oil skimming and bilge equipment will be available for collecting the spillage. Such equipment has, however, large inherent limitations with respect to efficiency, reliability or to temperature, wave or wind limitations.
Traditionally, a drilling unit is made with full venting and discharge to sea in order to get rid of uncontrolled leakage. The risks that undesired accidents may occur in waters close to shore makes traditional drilling platforms unsuitable for use in specific vulnerable and sensitive areas.
Several solutions for preventing such undesired leakage to the sea have previously been proposed. U.S. Pat. No. 3,698,198 describes an offshore platform of the type resting on the seabed and consisting of a plurality of assembled buoyancy bodies, stacked on top of each other. In assembled state the various buoyancy bodies are held together by tensioned cables, extending from the deck on the upper buoyancy body to the base structure resting on the seabed. Two adjoining sections may be interlocked by means of bolts and nuts. The offshore platform according to the US publication is also provided with a single cell extending between the deck, arranged above the sea level, and the base structure on the seabed. Drilling is performed from the deck, down through the vertical cell and down into the seabed, the vertical cell being with out a bottom. Each buoyancy body is provided with buoyancy chambers arranged around the vertical cell. Further, the sell has openings enabling water to be pumped from a neighboring body positioned below or on top. Each buoyancy body is also provided with downwards projecting parts at its lower end and co-acting upwards projecting locking elements at the upper surface of each buoyancy body, enabling installation and interlocking with a consecutive buoyancy body.
GB 2063776 relates to a solution for collecting oil and gas from a blow out where a umbrella-like body is lowered down over a leaking well, the umbrella-like body collecting oil and gas and allowing the leaked fluid to flow from the area of leakage into a vessel and/or to a flare means. Further, the umbrella-like means may be connected to an expandable cylindrical chute brought into place down and over the leaking area, so that a more or less shielded ring or cylinder is provided over and around the flow of leaking fluid.
Based on the discomfort as described above, there is a need for development of improved systems for collecting leaked hydrocarbons and a concept for protecting the environment, avoiding leakage of hydrocarbons to the sea and at the same time providing solutions which are rigid, stable and able to resist the environmental forces appearing at the offshore site.